This disclosure relates to a vaporized fuel processing apparatus having a failure detection function for a closing valve disposed on a path connecting a fuel tank with a canister.
Japanese Laid-Open Patent Publication No. 2004-156494 discloses a conventional vaporized fuel processing apparatus capable of detecting abnormality where a closing valve is left in a closed state. The apparatus opens the closing valve under a condition that a differential pressure between a tank inner pressure and the atmospheric pressure is beyond a predetermined reference value in a state that an internal combustion engine is stopped. In such procedure, when the amount of change in the inner pressure of the fuel tank is small, the apparatus determines that the closing valve is in a closed fastening state.
However, the apparatus should open the closing valve only for each failure detecting operation. Accordingly, there has been a need for improved vaporized fuel processing apparatuses.